凸起的固有形状
The intrinsic shape of bulges
摘要：
利用GASP 2D算法计算了148个无阻S 0-Sb星系的结构参数，并分析了星系核的内禀形状。我们开发了一种新的方法来推导出的内在形状的光度数据的基础上的鼓包和磁盘的表观和内在的形状之间的几何关系。该方法被认为是完全独立的研究类的对象，它可以适用于嵌入在轴对称组件的三轴椭球被认为是。我们发现，固有的形状是很好的约束的子样本的115个凸起有利的视角。它们中的大部分以椭圆截面为特征（B/A<0.9）。如果使用它们的最大、平均或中位赤道椭圆率，该分数分别为33%、55%和43%。它们中的大多数沿着极轴是扁平的。三轴度的分布是强烈的双峰。这种双峰性是由塞尔西克指数n>2的星系核球驱动的，或者等价地说，是由星系核球与总核球之比B/T>0.3的星系核球驱动的。n<2且B/T<0.3的凸起遵循类似的分布，这与n>2且B/T>0.3的凸起的分布不同。特别是，与n> 2和B/T> 0.3的凸起相比，n<2和B/T<0.3的凸起分别显示出更大比例的扁圆轴对称（或近轴对称）凸起、更小比例的三轴凸起和更少比例的扁长轴对称（或近轴对称）凸起。根据对鼓包形成的数值模拟，n<2的鼓包，表现出很高比例的扁圆轴对称（或近轴对称）形状，B/T<0.3，可能是耗散小合并的结果。对于n>2和B/T>0.3的凸起，似乎需要用主要的耗散和无耗散并合来解释所发现的各种形状。
英文摘要：
The structural parameters of a magnitude-limited sample of 148 unbarred S0-Sb galaxies were derived using the GASP2D algorithm and then analyzed to derive the intrinsic shape of their bulges. We developed a new method to derive the intrinsic shape of bulges based on photometric data and on the geometrical relationships between the apparent and intrinsic shapes of bulges and disks. The method is conceived as completely independent of the studied class of objects, and it can be applied whenever a triaxial ellipsoid embedded in an axisymmetric component is considered. We found that the intrinsic shape is well constrained for a subsample of 115 bulges with favorable viewing angles. A large fraction of them is characterized by an elliptical section (B/A<0.9). This fraction is 33%, 55%, and 43% if using their maximum, mean, or median equatorial ellipticity, respectively. Most of them are flattened along their polar axis. The distribution of triaxiality is strongly bimodal. This bimodality is driven by bulges with Sersic index n>2, or equivalently, by the bulges of galaxies with a bulge-to-total ratio B/T>0.3. Bulges with n<2 and with B/T<0.3 follow a similar distribution, which is different from that of bulges with n>2 and with B/T>0.3. In particular, bulges with n<2 and with B/T<0.3 show a larger fraction of oblate axisymmetric (or nearly axisymmetric) bulges, a smaller fraction of triaxial bulges, and fewer prolate axisymmetric (or nearly axisymmetric) bulges with respect to bulges with n>2 and with B/T>0.3, respectively. According to the numerical simulations of bulge formation, bulges with n<2, which show a high fraction of oblate axisymmetric (or nearly axisymmetric) shapes and have B/T<0.3, could be the result of dissipational minor mergers. Both major dissipational and dissipationless mergers seem to be required to explain the variety of shapes found for bulges with n>2 and B/T>0.3.
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